Mobile Telephony – GSM vs CDMA

Back in the 1990s, everyone had to use a landline telephone, fax, telegram or postal letters to communicate in Kenya. It required several days or weeks of planning just to organize for a meeting in Nairobi with a person from upcountry. Tracing a person was not easy, unlike now when a person can be ‘seen’ anytime anywhere using the mobile phone. These features of legacy communication methods adversely affected business operations; procurement processes took too long, landline access was limited to urban areas, collaboration between different branches of the organization remained challenging, response rate to customers was slow, advertising was not personalized and so on. The need for mobility was eminent and by the year 2000, mobile telephony providers had landed in Kenya. The rest of the world was rapidly adapting to this technology and in 2008 there were 4.1 billion mobile cellular subscriptions in the world.

Just to get an insight of how mobile telephony works, mobile phones send and receive radio signals with any number of cell site base stations fitted with microwave antennas. These sites are usually mounted on a tower, pole or building, located throughout populated areas, then connected to a cabled communication network and switching system. The phones have a low-power transceiver that transmits voice and data to the nearest cell sites. The most sophisticated aspect of mobile telephony is the fact that a mobile phone is able to switch seamlessly between sites. As the user moves around the network, the "handoffs" are performed to allow the device to switch sites without interrupting the call.

There are two main standards used in mobile telephony, Global System for Mobile communications (GSM) and Code division multiple access (CDMA). The two standards use different ideology to achieve the same goal: to divide the finite radio frequency spectrum among multiple users. Using an analogy, think of a cocktail party where different want to talk to each other. The first way of doing is have each person allocated a time slot to address the other person, this is how GSM functions. The second way is to have each pair of person talking in a different language, this is how CDMA functions. The first option may necessitate shorter speeches to give each person a chance to talk while second option may prove noisy if the pairs are too loud. Technically, GSM requires high frequencies to offer a high number of timeslots, up to 1.9 Ghz, while CDMA many suffer from interference if high amplitude codes are used at the same channel.

GSM is the more popular than CDMA with the technology adopted in 212 countries throughout the world. It rides on Time Division Multiple Access (TDMA) technology which is used to allow eight full-rate or sixteen half-rate speech channels per radio frequency channel. Newer versions of the standard are backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE). Recent third-generation (3G) releases have improved the data rates on the ‘smart’ mobile phones. The main advantage of GSM is that it offers international roaming, essential for traveling businessmen. Overall, this means low business operation costs and high efficiency.

On the other hand, CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. Many codes occupy the same channel, but only users associated with a particular code can understand each other. CDMA has several unique features that make it a cost-effective, high quality wireless solution. Each BTS in a CDMA network can use all available frequencies. Adjacent cells can transmit at the same frequency because users are separated by code channels, not frequency channels. This feature of CDMA, called "frequency reuse of one," eliminates the need for frequency planning. Generally, CDMA has better bandwidth utilization since the same channel can be used several users. This reduces the cost of implementation for a service provider rolling out a CDMA network. Reduced costs for a service provider may have a ripple in reduced cost of service to the customer. In addition, CDMA features result in coverage that is between 1.7 and 3 times that of TDMA .Coding and interleaving provide the ability to cover a larger area for the same amount of available power used in other systems. Finally, coding provides security for the conversations in a channel since each channel has its own code and an interfering device cannot decode it.

GSM still stands as the most popular while CDMA remains unexploited. In Kenya, there are 4 GSM providers; Safaricom, Zain, Orange and YU, and 3 CMDA providers; Orange Fixed Plus, Flashcom and Popote Wireless, but the number of subscribers for the two standards differ significantly.